Russia's Black Sea naval forces practiced destroying enemy targets on Tuesday as Moscow bristled at the presence of two U.S. warships in the area.
President Vladimir Putin said on Monday that Russian forces could observe the USS Mount Whitney navy command ship "through binoculars or in the crosshairs of its ... defense systems" and complained about NATO activity near Russia's borders.
On Tuesday, the Black Sea fleet said its ships had rehearsed destroying enemy targets and that their air defense systems had been put on alert at its bases in Novorossiysk and on annexed Crimea, the Interfax news agency reported.
"They ... destroyed airborne targets of a mock enemy with anti-aircraft missile weapons and artillery," it said in a statement.
Russia has previously warned Western countries against sending warships to the Black Sea and approaching the coast of Crimea, the peninsula it annexed from Ukraine in 2014. Russia considers Crimea part of its territory, but the peninsula is internationally recognized as part of Ukraine.
The U.S. Navy said on Monday that the USS Mount Whitney had arrived in Istanbul and that it would soon join forces with other ships in the Black Sea.
"Following this port visit, Mount Whitney will join USS Porter (DDG 78) in the Black Sea to further enhance collaboration between U.S. and NATO forces at sea," the U.S. Navy said in a statement.
The Kremlin on Tuesday rejected as a "low-quality fake" a U.S. media report about a Russian military buildup near Ukraine, although it said it was up to Moscow where it moved troops around on its territory.
The Politico news outlet reported that commercial satellite photos taken on Monday confirmed recent reports that Russia is once again massing troops and military equipment on the border with Ukraine after a major buildup this spring.
Ukraine said on Monday it had not observed any increase in Russian troops or equipment near the border.
A NATO official said: "NATO is vigilant and routinely monitors Russian force movements. It’s important to ensure transparency and avoid any miscalculation."
Russia has repeatedly accused NATO of carrying out provocative activities close to its borders. The alliance says it is determined to reinforce the security of member states close to Russia following Moscow's annexation of Crimea and its backing for pro-Russian rebels in eastern Ukraine.